In some ways, they are a typical political power couple seeking to “Make America Great Again.”

They are throwing a $5 million fund-raiser for President Trump this winter, and are quick to make it known that they have the president’s sons’ cellphone numbers on speed dial. They have poured more than $50,000 of their own money into supporting the president, who smiles in photos on the bookshelves of their home.

But Bill White and his husband, Bryan Eure, are not red state evangelicals or die-hard right-wingers. In fact, for years, they were key players among a cohort that Mr. Trump loathes: Manhattan’s liberal elite.

Mr. Trump is an unconventional commander in chief who ran an unorthodox campaign. As such, he has cultivated unusual allies, including Kanye West and Roger Stone. Mr. White and Mr. Eure used to back strident, anti-Trump Democrats, but now dine with Fox News anchors and plan rounds of golf at Mar-a-Lago.

The couple are standouts among the president’s small contingent of visible supporters in his hometown, New York City.

“He’s not a politician,” Mr. White, 51, said when asked to explain why he favors Mr. Trump. “He’s not going to configure himself as anything other than what he is. I think that he has an authenticity.”

Broad-shouldered with a silver buzz cut, Mr. White is a former president of the Intrepid Sea, Air and Space Museum in Manhattan, credited with bringing it back from financial collapse.

Mr. White parlayed that role into a little black book so thick that in 2011, he hired Aretha Franklin as the wedding singer at his marriage to Mr. Eure, where Democratic officials and Barbara Walters sang along with other guests at the Four Seasons restaurant in Manhattan.

The two men were not only longtime backers of left-wing causes, but firm supporters of Hillary Clinton who put their clout and cash behind her two White House bids. President Barack Obama was the guest of honor at a $39,500-a-plate truffle risotto fund-raiser dinner they hosted once in their Chelsea townhouse.

Mr. Eure, 39, a commercial insurance broker, grew up in North Carolina, and met and fell in love with Mr. White in an AOL chat room 18 years ago. A Republican, he nonetheless steered substantial sums to the liberal causes that his husband once supported.

The couple say they have been condemned not just for hypocrisy, but for what has been seen as a betrayal of their own community, by backing a man who has scaled back L.G.B.T. protections.

As they have risen in the Trump pantheon to attending cocktail parties with Trump acolytes, they’ve lost friends, the couple said, from liberal politicians they once lavished with campaign contributions to a former employee of Mr. White’s who sent excoriating Twitter messages.

Their former allies offer a succinct view on who Mr. Eure and Mr. White are now: craven turncoats.

“They ran to the other end of the spectrum and then walked off the ledge,” Nick Merrill, a spokesman for Mrs. Clinton, said. “This president is degrading our institutions. He is racist, he has no respect for women, he has no respect for minorities or for any community, including the L.G.B.T. community — it makes you wonder.”

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Mr. White and Mr. Eure have several photos of themselves with President Trump in their Atlanta home.CreditMelissa Golden for The New York Times

Mr. Merrill added: “Our democracy has been set on fire by this president, and they want what, an invite to Mar-a-Lago?”

At a dinner the couple hosted early this year in their Chelsea apartment, Corey Johnson, a Democrat and the openly gay speaker of the New York City Council, became irate when the couple suggested he meet Mr. Trump to discuss the city’s infrastructure needs, Mr. White said.

“It was like a food fight,” Mr. White said. “It was in our home, him calling us complete political idiots.”

Mr. Johnson declined to comment. The former friends have not spoken since, the couple said.

On the other side, there are few complaints about Mr. White and Mr. Eure’s switch.

“It happens whether you begin on the left or begin on the right, there’s always movement,” the former TV host Bill O’Reilly, a friend of the couple, said in an interview. “It represents considerable health in the country, not a disturbance or perturbation. It turns out they made a very smart decision.”

The genesis of the couple’s reversal can be timed to about midnight on Nov. 8, 2016. Inside the Jacob K. Javits Convention Center in Manhattan, at Ms. Clinton’s election night event, Mr. White stood watching the returns in an increasingly funereal atmosphere.

He got in his Chevrolet Suburban and drove to the New York Hilton in Midtown, where Mr. Trump was celebrating his win.

“I didn’t want to be part of that misery pie; I’m not a wallower in self-pity,” said Mr. White, who now runs Constellations Group, a strategic consultancy firm. “I really believe that once that decision is made, you have to get behind your president.”

“Exaggerations,” Mr. White added. “He’s the marketer in chief for the United States. So what?”

Since 2016, the couple has made a gradual shift from life in the liberal enclaves of the Hamptons and Manhattan, where they had long flipped homes as a hobby, to Atlanta, where they recently purchased property.

They now split their time between New York and Georgia. In the South, they are closer to Mr. Eure’s parents and found that they can wear red pro-Trump hats in peace.

Chatting inside their latest project, in the Buckhead neighborhood, they described a litany of slights by Democrats as motivation for switching sides.

There was the time, earlier this year, at Ralph Lauren’s Polo Bar in Midtown Manhattan, when Mr. White spotted Chelsea Clinton across the dining room.

Offended that she failed to acknowledge him, Mr. White said, he whipped out his phone and dialed Donald Trump Jr. “He said, ‘Do you want me to come over? I’m at the office, do you want me to?’”

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Mr. White acquired a Trump 2016 campaign button on election night after departing Hillary Clinton’s event in Manhattan.CreditMelissa Golden for The New York Times

Mr. White added: “Trump picks up on the first ring. If you want to get to Chelsea Clinton, you have to call through five people.”

Donald Trump Jr. acknowledged the two have become friends. “It’s much easier to be a sheep and buy into the narrative than it is to decide for yourself,” he said.

Then there was the time in 2016 when Mr. Eure said he had headed to Philadelphia from the Hamptons to watch Hillary Clinton speak at the Democratic National Convention.

A windstorm had grounded all the commercial aircraft, so he pulled gilded strings to borrow a friend’s helicopter, he said. But as the couple rushed to say hello to the candidate, a staffer blocked them.

“This was about because we didn’t write a $25,000 check” in the final stretch of her campaign, Mr. Eure said.

Ms. Clinton’s campaign rejected the claim.

“Some people give their time and resources to causes and candidates for the right reasons, some don’t,” Mr. Merrill, Ms. Clinton’s spokesman, said. “No better indication of which case this is than to watch a guy decide to embrace Trump and all he stands for because he couldn’t get his picture taken one night.”

Since boarding the Trump Train, as they call it, for every morsel of recognition the Trumps have offered, the couple has responded with a feast — sometimes literally.

Over the summer, they hosted a private dinner for Donald Trump Jr. and his girlfriend, Kimberly Guilfoyle, the former Fox News host. The occasion? Celebrating that the couple were dating.

For Mr. Eure, the fealty feels natural. The son of a chicken and soybean farmer who put himself through college, Mr. Eure sees his father as a parallel to Mr. Trump, whose oft-pushed narrative is that he is a self-made man — nevermind that the president’s story is false.

His husband also said Mr. Trump’s travails resonated.

In 2008, Mr. White abruptly resigned as president of the Intrepid, pushed out, he said, after the state began an investigation into whether he had engaged in unlicensed commercial fund-raising.

He was not charged with any crime, but agreed to pay $1 million in restitution to the state as a settlement.

Mr. White, who said he had done no wrong, still winces when he speaks of the pillorying that followed.

The pair said their behavior was in keeping with a lifelong focus on mission over party, namely fighting for veterans and gay rights.

They have supported a few Republicans before Mr. Trump. They’ve also jumped political ship: In 2012, they made headlines by demanding a refund from Mitt Romney, which they did not get, after the G.O.P. candidate for president said marriage was exclusively between a man and a woman.

And for Mr. Eure, the bumpy ride has been less of an evolution than a return to his Republican roots. “My parents are thrilled,” he said.

A version of this article appears in print on , on Page A19 of the New York edition with the headline: They Backed Clinton, Then Hitched Their Wagon to Trump. Order Reprints | Today’s Paper | Subscribe